The present disclosure relates generally to the routing of a telephone call from a mobile unit, and particularly to the routing of an emergency telephone call from a cellular phone in signal communication with a cellular telephone system.
Cellular telephones include an area code similar to land based telephones referred to as the Number Plan Area (NPA) code, which associates the cellular phone (cellphone) with a particular geographic location. When placing a call to or from a cellphone, the NPA code is used to associate the cellphone with a particular Service Control Point (SCP), which is a processing facility for managing the call connections. A cellphone having a NPA code in a first geographic region but being physically located in a second geographic region will have call features managed by the SCP in the first geographic region, even though the first geographic region may be located at a substantial distance from the actual location of the cellphone in the second geographic region. For a non-emergency cellphone call, this arrangement is appropriate for the purpose of providing cellphone features. However, for an emergency cellphone call it would be advantageous to have a cellular telephone system (CTS) capable of more effectively routing the emergency cellphone call.
In a landline emergency 911 (E911) system, an E911 tandem switch routes calls to the proper Public Safety Answering Point (PSAP) based on the Numbering Plan Area Code (NPA-NXX) of the calling number. Once the call arrives at the PSAP, the PSAP can access the Automatic Location Identification (ALI) database to obtain geographic mapping information about the location of the calling number, based on all 10 digits of the calling number.
Present Wireless E911 (WE911) system uses one to three “pseudo” phone numbers associated with each cell tower. WE911 calls using this system are routed to the PSAP on the basis of the phone number associated with the cell tower, using the E911 tandem described above. In response, the ALI database retrieves information about the cell site. Since the cell tower possibly uses more than one “pseudo” phone number, this system does not report the accurate location of the caller.
While some caller location information is available for wireless callers, improvement in the art is still needed for more effective WE911 call routing.